- regulates daily body rhythm (sleep)

- made of pinealocytes (covered by fibrous tissue from pia mater), glial cells, and calcified deposits (brain sand)

- responds to light and dark cycles via retinohypothalamic

- produces melanin during dark cycles

Pineal gland

- made of spheres of cuboidal cells (follicles) with central mass (colloid)

- follicles surrounded by basal lamina

- secretes T3 & T4 (regulates metabolism, fetal development, stimulates GH)

- regulated by TSH

- closely related to the parathyroid gland

Thyroid gland

- made up of follicular cells, parafollicular cells (C cells), and Colloid

- make thyroid hormones, calcitonin, and contains thyroglobulin

- removes iodide from blood, oxidizes it

Thyroid follicles

- lowers blood calcium levels by suppressing osteoclasts and promoting osteoid calcification

- produced by parafollicular cells (C cells)

Calcitonin

- usually 4 small glands closely associated with thyroid gland

- derived from 3rd and 4th branchial pouches

- composed of chief cells (smaller/darker) and oxyphil cells (larger/pinker)

- produces parathyroid hormone

Parathyroid glands

- increases serum calcium and decreases serum phosphate

- causes bone resorption (activates osteoclasts)

- decreases kidney excretion of calcium

- increases urinary phosphate excretion

- increases intestinal absorption of calcium

Parathyroid hormone

- paired endocrine glands combined into one structure

- medulla has dual blood supply

- veins drain to IVC and have more muscle than normal

- made of medulla and cortex

-produces catecholamines, mineralocorticoids, gonadal hormones, and glucocorticoids

Adrenal gland

- drain into medullary sinusoids

- one of the two adrenal medulla blood supplies

Cortical sinusoids

- drain into medullary sinusoids after traversing the cortex

- one of the two adrenal medulla blood supplies

Medullary arterioles

- have more muscle in their media than most veins

- contraction promotes increased movement of medullary blood into the circulation

Medullary veins

- arises from neural crest cells (modified sympathetic ganglion)

- made of chromaffin cells

- numerous myelinated presynaptic sympathetic nerves contact the chromaffin cells, stimulating release

- secretes catecholamines [(nor)epinephrine] and chromogranins

- more epinephrine than norepinephrine

Adrenal medulla

- conversion of norepinephrine to epinephrine is stimulated by these

glucocorticoids

- arises from mesodermal mesenchyme

- has three layers (zona glomerulosa, fasciculate, reticularis)

- secrete mineralocorticoids, glucocorticoids, gonadal hormones respectively

Adrenal cortex

- outermost layer of adrenal cortex

- looks like "round balls"

- secretes mineralocorticoids (aldosterone)

- regulated by renin-angiotensin II-aldosterone system

Zona glomerulosa

- mid portion of cortex

- looks like "long cords" or fascicles

- secretes glucocorticoids (cortisol)

- regulated by CRH-ACTH hypothalamic-pituitary system

Zona fasciculate

- innermost of cortical zones

- looks like interconnected cords of cells (reticulum)

- secrete gonadal hormones (DHEA)

- regulated by CRH-ACTH

Zona reticularis

- usually part of a mucosa or other viscera

- specific to the region they're located in

- usually neural crest in origin

- have dense-core secretory granules seen on ultrastructure (contain chromogranins)

Diffuse neuroendocrine system